Motor-vehicle rear suspension

ABSTRACT

There is described a motor vehicle rear suspension comprising, for each wheel, a longitudinal arm carrying the wheel and pivotally mounted onto the fixed structure of the motor vehicle around a transverse axis. The arm includes a torsionally deformable blade arranged substantially in a longitudinal vertical plane and an auxiliary arm connected to the fixed structure of the motor vehicle with the interposition of an articulated rod element and is further connected to the fixed structure of the motor vehicle by means of a transverse rod.

BACKGROUND OF THE INVENTION

The present invention relates to motor-vehicle rear suspensions of thetype which comprises, for each wheel:

a longitudinal arm, having one end pivotally mounted on the fixedstructure of the motor-vehicle around an axis directed transversally tothe longitudinal direction of the motor-vehicle and the opposite endcarrying a respective wheel hub,

an auxiliary arm connected to the longitudinal arm and having one endconnected to the fixed structure of the motor-vehicle,

an articulated rod element interposed in the connection between theauxiliary arm and the fixed structure of the motor-vehicle,

a further connecting rod interposed between a longitudinal arm and thefixed structure of the motor-vehicle and directed transversally to thelongitudinal direction of the motor-vehicle, and

resilient and damping means interposed between the longitudinal arm andthe fixed structure of the motor-vehicle.

A suspension of the above indicated type is for instance described andillustrated in German patent application DE-A-34 26 942.

SUMMARY OF THE INVENTION

The object of the present invention is that of providing a motor-vehiclerear suspension of the above indicated type which has reduced dimensionsand weight while insuring a good behaviour of the motor-vehicle in anytravel condition.

In order to achieve this object, the invention provides a rearsuspension of the above indicated type, characterized in that theportion of the longitudinal arm which is pivotally mounted around saidtransverse axis on the fixed structure of the motor-vehicle isconstituted by a torsionally deformable blade, arranged substantially ina vertical longitudinal plane, in that said resilient means areconstituted by a torsion bar directed along said transverse articulationaxis of the longitudinal arm, said torsion bar having one end anchoredto the fixed structure of the motor-vehicle and the opposite end rigidlyconnected to said blade, and in that the torsion bar is of tubular shapeand has inside thereof an anti-rolling bar rigidly connected at its endsto the blades associated with the two longitudinal arms of thesuspension.

In a preferred embodiment, the blade and said articulated rod elementare connected to a frame on which they are pre-assembled, this framebeing fixed to, the fixed structure of the motor-vehicle and including ahollow cylindrical body directed along said transverse axis, insidewhich the end of said torsion bar which is anchored to said blade isrotatably mounted. It is to be noted that rear suspensions havinglongitudinal arms in forms of blades are known also from DE-A-2 123 666,DE-B-1 162 702, FR-A-2 400 441. However, the above defined structure andarrangement of the suspension of the present invention is notanticipated nor suggested by the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be now described with reference to the annexeddrawings, given purely by way of non limiting example, in which:

FIG. 1 is a perspective view of the portion of the motor-vehicle rearsuspension according to the invention which is associated with the leftrear wheel of the motor-vehicle,

FIG. 2 is a plan view of the device of FIG. 1,

FIG. 3 is an elevational side view of the device of the FIG. 1, and

FIG. 4 is a diagrammatic representation of the kinematic arrangementprovided with the suspension according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, there is illustrated a preferred embodiment of thesuspension according to the invention in which the various portions ofthe suspension are mounted on two auxiliary frames 1, 2 which on theirturn are fixed to the motor-vehicle structure. It is thus possible,according to a technique known per se, to pre-assemble the various partsof the suspension on the auxiliary frames 1, 2 and then to assemble in asingle operation the whole assembly constituted by the auxiliary frames1, 2 and the suspension on the motor-vehicle structure. Naturally,however, the invention is applicable also by providing auxiliary frameshaving a shape different from that shown in the drawings, or a singleauxiliary frame which supports all the various components of thesuspension, or even by having the various parts of the suspension beingmounted onto the motor-vehicle structure.

In the case of the illustrated example, the auxiliary frame 1 comprisesa hollow cylindrical body 3 arranged along an axis x which is directedtransversally to the longitudinal direction of the motor-vehicle (inFIG. 2, arrow A designates the direction of movement). The hollowcylindrical body 3 is supported at each end by a pair of arms 4, 5 whichextend respectively along a substantially longitudinal directionforwardly and rearwardly of the hollow cylindrical body 3 and have theirends connected to body S of the motor-vehicle (shown with dotted linesin FIG. 3) by means of rubber damping supports 6, 7.

The auxiliary frame 2 is constituted by a cross-member structure havingeach of its ends screwed to body S by screws 8.

The reference 9 generally designates the structure of a longitudinal armhaving one rear end connected to a wheel support 10 which rotatablysupports the hub 11 of a wheel 12 around an axis r.

The longitudinal arm 9 is pivotally mounted around axis x onto theauxiliary frame 1. In the embodiment shown in the drawings, this pivotalassembling is provided by a torsionally deformable blade 13 which isarranged substantially in a vertical longitudinal plane and has one endrigidly connected by screws 14 to a structure 15 forming the body of thelongitudinal arm 9. The opposite end of blade 13 is welded and fixed bya bolt 16 to a plate 17 (FIG. 2) which is rigidly connected to a bush 18which is rotatably supported around axis x by the auxiliary frame 1, bymeans of bearings 19. The blade 13 may also be mounted in a pre-loadedcondition. Yet in the illustrated embodiment, a torsion bar 20 oftubular shape is arranged inside the hollow cylindrical body 3 with itsaxis coincident with axis x and has one end rigidly anchored to thecentral part 3a of the hollow cylindrical body 3, and an outer endrotatably connected by a fluted coupling to bush 18. The torsion bar 20thus acts as a spring means for opposing any articulation movement ofthe longitudinal arm 9 around axis x. Naturally, a symmetricalarrangement is provided for the other rear wheel of the motor-vehicle.Yet in this specific embodiment which is shown in the drawings, insideof the two torsion bars 20 associated with the two rear wheels of themotor-vehicle there extends an anti-rolling torsion bar 21 whoseopposite ends are each rigidly connected to the respective bush 18. Theanti-rolling bar 21 tends to oppose asymmetrical articulation movementsof the two longitudinal arms 9 around axis x.

In the suspension according to the invention, each longitudinal arm 9 isfurther provided with an auxiliary arm 22 (which in the illustratedexample is formed in one piece with body 15) ending with one endconnected to one bracket 3b (FIG. 1) welded to the hollow cylindricalbody 3 outside thereof by an articulated rod element 23. The articulatedrod element 23 is constituted by a push-rod adjustable in length by ascrew system articulated at its ends to bracket 3b and to the auxiliaryarm 22.

Although in the case of the illustrated example blade 13 is constitutedby a separate element which is rigidly connected to body 15 of thelongitudinal arm 9, this blade may be constituted, at leasttheoretically, by an element integrated into the body of thelongitudinal arm. At the same time, the auxiliary arm 22 could also beconstituted by a separate element rigidly connected to body 15 of thelongitudinal arm. The longitudinal arm 9 is further provided with abracket 9a for connection of the lower end of a damping cylinder 24whose upper end is to be connected to body S of the motor-vehicle.

Finally, to the longitudinal arm 9 there is associated a transverse rod25, adjustable in length, having its ends respectively articulated at 26to the wheel support 10, at an area spaced apart from axis r of thewheel, and at 27 to the auxiliary frame 2, adjacent to the mediumlongitudinal plane M of the motor-vehicle (FIG. 2).

The operation of the above described suspension will be now discussed.

The longitudinal arm 9 is guided in its articulation movements aroundaxis x by the transverse rod 25 and the articulated rod element 23. Byvarying the length of rod 23 the theoretical camber angle of the wheelmay be adjusted. By varying the length of the transverse rod 25 thetheoretical wheel toe-in angle is adjusted.

When the motor-vehicle is travelling, during the movements along thevertical direction of the wheel with respects to the motor-vehicle body,the longitudinal arm 9 is on one hand forced to rotate around axis x andat the same time is also forced to move around the articulation 23b ofthe articulated rod element 23 and articulation 27 of the transverse rod25. As a result of this, the whole structure of the longitudinal arm 9moves around a theoretical spherical centre 1CS. The arm 9 is able totilt around this spherical centre 1CS due to the possibility of blade 13to be torsionally deformed around its neutral axis y1. The sphericalcentre 1CS is identified by the intersection of this axis y1 with axisx. By y2 the axis is identified which joins centre 1CS to articulation26 of the transverse rod 25 on the longitudinal arm 9. The rotation axisd of the transverse rod 25 is formed by the line joining articulation 27of rod 25 on auxiliary frame 2 to the spherical centre 1CS. With theabove described geometry, for each instantaneous movement there existsan instantaneous rotational axis which passes through the sphericalcentre 1CS and the articulation instantaneous centre Ci of the wheel inthe transverse plane containing the wheel axis. The instantaneousrotational axis ai, in a theoretical condition, must have the same angleof the wheel axis r with respect to the horizontal plane. This principleinsures the linear variation of toe-in angle and the camber angle as afunction of the wheel movement. If the instantaneous rotation axis ai ina theoretical condition is inclined downwardly, during upward movementof the wheel, an oversteering effect takes place (divergence); if saidaxis is inclined upwardly an understeering effect takes place(convergence). Straight line b and straight line c shown in FIG. 1 haveorigin in spherical centre 1CS and pass through ends 23a, 23b of thearticulated rod element 23. These straight lines b, c cross thetransverse plane containing axis r of the wheel (FIG. 4) at two pointsn, m whose joining line is a vertical line containing the instantaneousrotation centre Ci. The kinematic arrangement remains unvaried when theshape of the various components of the suspension is varied, providedthat said axes remain the same.

Yet with reference to FIG. 4, the illustrated kinematic arrangementsubstantially corresponds to a rigid body which has a spherical joint toa fixed point 1CS and is connected by spherical joints 3a and 26 to tworigid levers 23 and 25 which are hinged by spherical joints respectivelyat two fixed points 23b and 27. For a kinematic arrangement of thistype, the instantaneous rotation axis ai is defined by the intersectionof the planes respectively containing points (1CS-3a-23b) and(1CS-27-26). The straight line intersecting these two planes has thefeature of being simultaneously orthogonal to the speed vectors of 3aand 26; i.e. the movement of 3a and 26 is a pure rotation around thisstraight line ai which therefore is the instantaneous rotation axis. 3aand 26 can not move, since they are rigidly connected to 1CS, which is afixed point.

The pitching centre CB is determined by the intersection of theinstantaneous axis ai with the longitudinal plane of the wheel. It isadvantageous that centre 1CS is as close as possible to the wheellongitudinal plane and as high as possible in order to increase the"anti-dive" characteristic of the suspension (i.e. the capacity ofopposing a forward pitching movement of the motor-vehicle when braking),this characteristic being directly proportional to angle β (FIG. 4)formed by the longitudinal horizontal direction with the straight linejoining centre CB to the contact point of the wheel on the ground.

The linearity characteristic of the variation of the toe-in angle andthe camber angle is kept if the oscillating movement of theinstantaneous rotation axis ai projected on a transverse planecorresponds to the variation of the camber angle. If the instantaneousrotation axis ai takes an oscillating movement around the sphericalcentre 1CS, the instantaneous rotation centre Ci moves along thestraight line joining points n and m, upwardly and downwardly, as afunction of the wheel movement. If the movement takes place with thesame time and space values of the wheel movement a condition with astable rolling centre CR is generated; i.e. the distance of the rollingcentre CR from the centre of gravity G is substantially the same duringthe wheel movement. In order to provide this condition it isadvantageous that in a theoretical condition the longitudinal planemeets the transverse plane containing the instantaneous rotation centreCi at a distance D which is at least twice the length L of thetransverse rod.

With reference to FIG. 2, when a lateral force F is present, the lateralyield of the blade 13 enables the longitudinal arm 9 to rotate clockwise(with reference to FIG. 2) with the articulation 26 as rotation centre.This effect gives raise to a toe-in of the wheels with resultingundersteering.

Due to the above described features, the suspension system according tothe invention satisfies the object of reduced dimensions, reduced weightand a good kinematic and elastic-kinematic behaviour, with camber beingtaken up during wheel movements, toe-in being controlled during wheelmovements and during a curve and with a stable rolling centre.

In the case of the preferred embodiment which has been illustrated,which uses the two torsion bars 20 combined with the torsionallydeformable blade 13 as resilient means, further advantages are obtained.For example, it is possible to use this suspension with motor-vehicleswith a low floor panel, since it is not necessary to provide asupporting structure for a helical spring. Furthermore, theelastic-kinematic behaviour of the suspension during travel of thevehicle in a curve is such that a variation of positive toe-in of theouterside of the curve is obtained (understeering). Also a bestdistribution of the forces among the various elements is obtained, thusfavouring a reduction of their weight.

However, the invention is also applicable to a suspension usingresilient means of a type different from that shown in the annexeddrawings, for example in the form of a helical spring interposed betweeneach longitudinal arm 9 and the fixed structure of the motor-vehicle.

In the case of the preferred embodiment with a torsion bar, blade 13 andtorsion bar 14 operate as two springs in parallel. By designing thegeometry of the system and the dimensions of blade and torsion bar, itis therefore possible, at least theoretically, to distribute therigidity between blade and torsion bar. Naturally, while the principleof the invention remains the same, the details of the construction andthe embodiments may widely vary with respects to what has been describedand illustrated purely by way of example, without departing from thescope of the present invention.

What is claimed is:
 1. Motor-vehicle rear suspension, comprising, foreach wheel:a longitudinal arm (9) having one end pivotally mounted ontothe fixed structure (S) of the motor-vehicle around an axis (x) directedtransversally to the longitudinal direction (A) of the motor-vehicle andone end carrying a respective wheel hub (11) an auxiliary arm (22)connected at one end to the longitudinal arm (9) and having the oppositeend connected to the fixed structure (S) of the motor-vehicle, anarticulated rod element (23) having one end articulated to the fixedstructure around a first axis and an opposite end articulated to saidauxiliary arm (22) around a second axis spaced from the first axis, afurther connecting rod (25) having one end articulated to thelongitudinal arm (9) and an opposite end articulated to the fixedstructure (S) of the motor-vehicle at a location spaced from saidarticulated rod and directed tranversally to the longitudinal direction(A) of the motor-vehicle, and resilient and damping means interposedbetween the longitudinal arm (9) and the fixed structure (S) of themotor-vehicle, characterized in that the portion of the longitudinal arm(9) which is pivotally mounted around said transverse axis (x) on thefixed structure (S) of the motor-vehicle is constituted by a torsionallydeformable blade (13), arranged substantially in a longitudinal verticalplane, in that the resilient means are constituted by a torsion bar (20)directed along said transverse articulation axis (x) of the longitudinalarm (9), said torsion bar (20) having one end anchored to the fixedstructure (S) of the motor-vehicle and the opposite end rigidlyconnected to the said blade (13) and in that said torsion bar (20) has atubular shape and has inside thereof an anti-rolling bar (21) rigidlyconnected at its ends to the two blades (13) associated with the tworear wheels of the motor-vehicle.
 2. Suspension according to claim 1,characterized in that said blade (13) and said articulated rod element(23) are connected to one auxiliary frame (1) which in turn is fixed tothe fixed structure (S) of the motor-vehicle, this auxiliary frame (1)including a hollow cylindrical body (3) having its axis coincident withsaid transverse axis (x), inside of which there is rotatably mountedsaid end of the torsion bar (20) to which the blade (13) is anchored.